Exhaust gas muffler having a spark arrestor screen

ABSTRACT

A muffler for the exhaust gas of an internal combustion engine is provided. The muffler has a housing with an inlet opening and an outlet, and surrounds a muffling chamber. In the flow path of the exhaust gas a spark arrestor screen, and on the side of the inlet opening an exhaust gas diffuser, are provided. The muffling chamber is divided by a partition into a first and second partial chamber. The volume of the second partial chamber corresponds at least approximately to the volume of the first partial chamber. The spark arrestor screen is disposed in the partition.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a muffler for the exhaust gas of an internal combustion engine, especially in a manually guided implement such as a power chain saw or the like, and includes a muffler housing that surrounds a muffling chamber and has an inlet opening and an outlet for the engine exhaust gas, whereby in the flow path of the exhaust gas a spark arrestor screen as well as, on the side of the inlet opening, an exhaust gas diffuser are provided.

[0002] In order to retain particles contained in the exhaust gas, a spark arrestor screen is disposed in the mufflers of motor-driven implements such as chain saws, brush cutters, suction devices/blowers, or the like. Such spark arrestor screens, which are disposed in the flow path of the exhaust gas, are subjected to high mechanical stresses due to temperature and pressure fluctuations.

[0003] U.S. Pat. No. 4,370,855 discloses a muffler of a power chain saw, according to which an exhaust gas diffuser in the form of a plate having many holes is disposed in the flow path of the exhaust gas on the side of the inlet opening. In the region of its holes, the exhaust gas diffuser is surrounded by a tubular spark arrestor screen. Along its flow path, the exhaust gas first passes the inlet opening, and subsequently the holes of the exhaust gas diffuser. In so doing, the pressure of the exhaust gas is partially relieved, and the noise level drops. After passing through the spark arrestor screen, the exhaust gas passes into the interior of the muffler, where a further drop in pressure occurs, before the exhaust gas flows through the outlet into the atmosphere. The flow velocity of the exhaust gas is relatively high in the individual openings of the exhaust gas diffuser, whereby the spark arrestor screen is subjected to high mechanical stress due to these high flow velocities. Due to the close arrangement of the spark arrestor screen on the exhaust gas outlet of the cylinder, the temperature level, as well as the pressure level, are very high, which can lead to a premature failure of the spark arrestor screen. The then necessary replacement of the spark arrestor screen is complicated and time consuming, since it is necessary to disassemble the muffler.

[0004] DE-OS 25 39 516 discloses a muffler where a spark arrestor grating is disposed in the vicinity of the muffler outlet. Unfortunately, such gratings tend to get clogged with soot and residue, since the exhaust gas stream in the vicinity of the outlet has an already reduced, low temperature. Oil or soot residues that are carried along in the exhaust gas stream settle on the grating, whereby the temperature of the exhaust gas stream is not sufficient to burn off the resulting deposits.

[0005] It is therefore an object of the present invention to improve a muffler of the aforementioned general type in such a way that the service life of a spark arrestor screen is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which:

[0007]FIG. 1 is a cross-sectional view through one exemplary embodiment of an inventive exhaust gas muffler showing the flow path of the exhaust gas; and

[0008]FIG. 2 is an exploded view of the individual components of the muffler embodiment of FIG. 1 showing structural details.

SUMMARY OF THE INVENTION

[0009] The muffler of the present invention is characterized primarily in that the muffling chamber is divided by a partition into a first partial chamber and a second partial chamber, wherein the volume of the second partial chamber corresponds at least approximately to the volume of the first partial chamber, and wherein the spark arrestor screen is disposed in the partition between the first and second partial chambers.

[0010] The basic concept of the present invention is to dispose a spark arrestor screen in an exhaust gas muffler in such a way that on the one hand the pressure of the exhaust gas stream is adequately reduced in the muffler, and the acoustic pressure peaks are smoothed to such an extent that mechanical overloading of the spark arrestor screen is reliably prevented. On the other hand, at the location where the spark arrestor screen is mounted the temperature level of the exhaust gas stream is sufficiently high, so that retained oil or soot particles are burned, thus reliably avoiding clogging of the spark arrestor screen.

[0011] Pursuant to the present invention, the muffling chamber is divided by a partition into two partial chambers, which are interconnected by an opening in which is disposed the spark arrestor screen. A so-called exhaust gas diffuser having a plate that is provided with a plurality of holes and is disposed in the region of the inlet opening generates a first stage for the pressure relief and smoothing of the acoustic pressure peaks in the exhaust gas stream. After passing the exhaust gas diffuser the exhaust gas stream enters the first of the two partial chambers, whereby the individual partial streams through the individual holes of the exhaust gas diffuser are combined in the partial chamber with a reduced overall pressure and lower acoustic pressure peaks. After this acoustic smoothing process, the exhaust gas stream passes through the spark arrestor screen into the second partial chamber, in which a further pressure relief is effected. Finally, upon discharge via the outlet, the exhaust gas stream is relieved to the pressure level of the atmosphere. With this cascade-like relief process between the high pressure at the exhaust gas outlet of the cylinder, i.e. at the inlet opening of the muffler housing, and the atmosphere, there is, at the passage between the first partial chamber, following the exhaust gas diffuser, and the second partial chamber a temperature level at which residue on the spark arrestor screen can still be reliably burned. By means of the exhaust gas diffuser and the first partial chamber, the pressure of the exhaust gas stream is relieved to such an extent, and the acoustic pressure peaks are smoothed to such an extent, that the mechanical stress of the spark arrestor screen is lowered. To produce an appropriate temperature and pressure level, the volume of the second partial chamber is at least approximately as great as the volume of the first partial chamber, and advantageously corresponds to the volume of the first partial chamber together with the volume of the exhaust gas diffuser.

[0012] Pursuant to one preferred specific embodiment of the present invention, the partition between the first and second partial chambers is also a wall portion of the exhaust gas diffuser. This wall portion is significantly heated up by the still very hot exhaust gas stream that enters the exhaust gas diffuser via the inlet opening. As a consequence of heat conduction in the partition, the spark arrestor screen that is held therein is reliably maintained at a high temperature level to avoid soot residue and clogging.

[0013] A simple solution to reduce manufacturing costs is provided by positively holding the spark arrestor screen in the partition in the flow-through direction. For this purpose, a holding means is preferably disposed on the partition into which the spark arrestor screen can be inserted and which at least partially engages around the periphery of the screen. To reduce the number of components, and hence the material and manufacturing costs, the exhaust gas diffuser is formed from the appropriately embodied partition on which is mounted an additional baffle plate that delimits the interior of the exhaust gas diffuser. The partition, and the baffle plate secured thereon, advantageously each have a ridge or shoulder that together form the retaining means. This eliminates the necessity for embodying the retaining means as a separate component.

[0014] To reduce maintenance costs, the muffler housing has a mounting slot through which the spark arrestor screen can be inserted into the retaining means. Consequently, for cleaning or replacement purposes the spark arrestor screen can be removed from and reinserted into the muffler housing without having to disassemble the housing. The spark arrestor screen is reliably secured on the muffler housing with little expense by means of a screw, and in particular by means of a self-tapping sheet metal screw.

[0015] The muffler housing is preferably formed from two partial shells or housing sections that are interconnected along a circumferential seam or joint, and at the same time are also connected with the partition. In particular by means of a flange-over, the essential components of the muffler can thus be interconnected in a single operation. The circumferential seam or joint is advantageously embodied in such a way that it is disposed in a single plane. As a result, the connection tool can have a simple design, especially for an automated manufacture. The spark arrestor screen, which can be inserted from the outside, is expediently provided with an angled-off retaining portion that engages about the circumferential joint. Consequently, the spark arrestor screen is additionally positively held also in the region of the mounting slot.

[0016] Further specific features of the present invention will be described in detail subsequently.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0017] Referring now to the drawings in detail, it can be seen from FIG. 1 that a muffler housing 2 surrounds an attenuation or muffling chamber 1 that is divided by a partition 8 into a first partial chamber 9 and a second partial chamber 10. The muffler housing 2 comprises a first partial shell or housing section 12 and a second partial shell or housing section 13 that are interconnected at a plane of separation 15 in common with the partition 8. Such a connection can be effected by welding, brazing or the like, and in the illustrated embodiment is formed by a flanged-over seam or joint 14. In the first housing section 12, an inlet opening 3 is provided for the exhaust gas stream; this inlet opening is formed by an annular collar 25. The partition 8 is provided with a tubular neck 26 that extends about the collar 25 and is connected therewith. A baffle plate 20 is secured to the partition 8 on that side opposite the inlet opening 3 or neck 26. The baffle plate 20, together with the neck 26, surround the interior 19 of an exhaust gas diffuser 7, whereby a wall portion 11 of the exhaust gas diffuser 7 is provided with a plurality of diffuser openings 27, which are shown in greater detail in FIG. 2. Furthermore provided in the partition 8 is a screen opening 28 for receiving a spark arrestor screen 6. The second housing section 13 of the muffler housing 2 is provided with an exhaust gas stream outlet 4 that is covered by an outlet hood 30.

[0018] The path of the flow of the exhaust gas is illustrated by the arrows 5, according to which the exhaust gas stream first passes via the inlet opening 3 into the interior 19 of the exhaust gas diffuser 7. For this purpose, the muffler is fixed in position directly on the exhaust port of the cylinder. By passing through a number of diffuser openings 27 in the first partial chamber 9, there is effected a drop in pressure of the exhaust gas and a smoothing of the acoustic pressure peak. Subsequently, the exhaust gas stream is conveyed, by the spark arrestor screen 6 in the screen opening 28, into the second partial chamber 10, whereby a further drop in pressure occurs. The exhaust gas stream finally passes through the outlet 4 into the atmosphere. The individual partial streams that pass through the plurality of diffuser openings 27 are combined in the first partial chamber 9, whereby the relatively large volume of this first partial chamber 9 initially leads to a reduction in the flow velocity. In comparison to the first partial chamber 9, the screen opening 28 has a small cross-sectional area, resulting in a re-acceleration of the exhaust gas stream which, however, no longer has the high acoustic pressure peaks as in the region of the exhaust gas diffuser. Due to the high flow velocity through the spark arrestor screen 6, the cleaning effect of the high temperature is enhanced, whereby the reduced pressure peaks prevent a mechanical overloading of the spark arrestor screen 6. To adapt the pressure and temperature level of the exhaust gas stream in the region of the spark arrestor screen 6, the volume of the second partial chamber 10 is at least approximately as great as the volume of the first partial chamber 9, and in the illustrated embodiment is approximately as great as the volume of the first partial chamber 9 together with the volume of the interior 19 of the exhaust gas diffuser 7. Due to the unitary configuration of the partition 8 with the wall portion 11 and the mounting of the baffle plate 20 to the partition 8, a good thermal connection of the spark arrestor screen 6 with the exhaust gas diffuser 7 is provided.

[0019] The spark arrestor screen 6 can be screw-connected with the partition 8, and in the illustrated embodiment is positively held by a retaining means 16 in the direction of the flow through direction, which is illustrated by the arrow 24. The retaining means 16 is formed by a respective ridge or shoulder 17, 18 of the partition 8 and the baffle plate 20 respectively, between which the spark screen 6 is inserted from the outside through the mounting slot 21.

[0020] The exploded view of FIG. 2 shows the structural details of the individual components of the muffler of FIG. 1. The first and second housing sections 12, 13, the partition 8, the baffle plate 20, as well as the outlet hood 30 are embodied as stamped, punched, or deep drawn sheet metal parts. Monolithically formed on the first housing section 12, in the region of the inlet opening 3, is the collar 25, to which is secured the neck 26, which is monolithically formed with the partition 8. The partition 8 is provided with a recessed portion that surrounds the neck 26 and forms the wall portion 11 of the exhaust gas diffuser 7 that is shown in FIG. 1. The plurality of diffuser openings 27 are provided in this wall portion 11. Also provided in the partition 8 is the screen opening 28, which is bordered by the ridge 17 in the region that does not adjoin the joint 14 (see FIG. 1). The ridge 17, together with the ridge 18 of the baffle plate 20, form the retaining means 16 (FIG. 1) for the spark arrestor screen 6. Instead of the ridges or shoulders 17, 18, retaining tabs or the like can also be advantageously formed on the partition 8 as separate parts or can be integral therewith. The second housing section 13 is provided between its edge that forms the joint 14, and the outlet 4, with the mounting slot 21 through which the spark arrestor screen 6 can be guided. The spark arrestor screen 6 is monolithically formed from a stamped wire mesh, and is provided with an angled-off retaining portion 22. When the spark arrestor screen 6 has been inserted into the mounting slot 21, it is secured to the muffler housing 2 via a screw 23. In the illustrated embodiment, the screw 23 is embodied as a self-tapping sheet metal screw 23 that engages in a screw hole 29 of the first housing section 12. In so doing, the angled-off retaining portion 22 engages around the seam or joint 14 and thus represents an additional positive connection of the spark arrestor screen 6 with the muffler housing 2.

[0021] The specification incorporates by reference the disclosure of German priority document 100 20 373.6 of Apr. 26, 2000.

[0022] The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims. 

What I claim is:
 1. A muffler for the exhaust gas of an internal combustion engine, comprising: a muffler housing that surrounds a muffling chamber, wherein said muffler housing has an inlet opening and an outlet for exhaust gas; an exhaust gas diffuser disposed in said muffler housing for receiving exhaust gas from said inlet opening; a partition disposed in said muffler housing to divide said muffling chamber into a first partial chamber and a second partial chamber, wherein said first partial chamber receives exhaust gas from said exhaust gas diffuser, and wherein said second partial chamber has a volume that corresponds at least approximately to a volume of said first partial chamber; and a spark arrestor screen disposed in said partition in a flow path of exhaust gas from said first partial chamber to said second partial chamber.
 2. A muffler according to claim 1 , wherein the volume of said second partial chamber corresponds approximately to the sum of the volumes of said first partial chamber and of said exhaust gas diffuser.
 3. A muffler according to claim 1 , wherein said partition forms a wall portion of said exhaust gas diffuser.
 4. A muffler according to claim 1 , wherein said muffler housing comprises two housing sections that are connected to one another and with said partition along a circumferential seam or joint.
 5. A muffler according to claim 4 , wherein said circumferential joint is disposed in a single plane of separation.
 6. A muffler according to claim 4 , wherein said housing sections and said partition are interconnected via flanged-over means.
 7. A muffler according to claim 4 , wherein means are provided for positively holding said spark arrestor screen in a flow through direction (24).
 8. A muffler according to claim 7 , wherein said means for holding is disposed on said partition and at least partially extends about a circumference of said spark arrestor screen.
 9. A muffler according to claim 8 , wherein a baffle plate is secured on said partition and delimits an interior of said exhaust gas diffuser, and wherein said means for holding is formed by a first shoulder of said partition and by a second shoulder of said baffle plate.
 10. A muffler according to claim 7 , wherein said muffler housing is provided with a mounting slot through which said spark arrestor screen is insertable.
 11. A muffler according to claim 10 , wherein said spark arrestor screen is provided with an angled-off retaining portion that engages about said circumferential joint.
 12. A muffler according to claim 10 , wherein a screw is provided for securing said spark arrestor screen to said muffler housing.
 13. A muffler according to claim 12 , wherein said screw is a self-tapping sheet metal screw. 